One day, a movie will be made about ‘Missile’ Missy Franklin. It might not be a midsummer blockbuster, it might not even be an art-house sleeper hit unmasking the mysteries of international swimming, but it will be underpinned by an intrinsically flawless script.

And as Sir Alfred Hitchcock observed: “To make a great film you need three things – the script, the script and the script.”

Franklin’s 18 years of life already harbour a plenitude of Hollywood virtues: a character to whom we warm instinctively; a pleasing contrast of humble origins with vast personal accomplishment; and a lesser-known undercurrent of tragedy.

This ebullient teenager, the ‘porpoise from Pasadena’ – born in California, she is technically based in Colorado – bestrides the world championship pool in Barcelona by her quest for seven gold medals, and yet she carries none of the entourage such star billing might imply.

In the cavernous stands of the Palau Sant Jordi she has only her parents, Dick and D.A., plus coach Todd Schmitz, who has mentored her since the age of seven, under the umbrella of a club without even its own pool.

But if this sounds like an implausibly idyllic existence on the homestead, it pays to be reminded of the harrowing recent past of Aurora, the Denver suburb where Franklin just attended her high-school prom and where James Holmes last summer shot dead 12 theatregoers.

“I’m so shaken by it,” she says. “Every single race I’m going to have it at the back of my mind.”

While Franklin’s narrative arc moves at warp speed, the anguish of the Aurora incident remains raw. Seven golds: the ambition would be colossal at any age, let alone for a young woman still to complete her college enrolment. To think it could have been eight, until she jettisoned the 50 metres backstroke to concentrate on her triumph on Wednesday night in the 200 metres freestyle.

When Michael Phelps delivered his octuple at the Beijing Games, Mark Spitz, whose record of seven in Munich was eclipsed, described it as “epic” and heralded the swimmer as “not only the greatest Olympian of all time, but maybe also the greatest athlete of all time”.

Phelps, reduced since 2012 to a mere bystander as he sits pretty upon his 18 Olympic golds, sets the bar ominously high for Franklin in terms of cinematic perfection in sport.

His storyline had it all: the battle with attention-deficit disorder, the single mother who raised him and his two sisters on a modest Baltimore wage, the Beijing coronation, the marijuana bust, and finally the London valediction.

There is a perception that Franklin is perhaps too glossy, too vacuum-formed a champion, to merit an immediate parallel. But while her seamless advance might be yet to hit any roadblock or controversy, it derives a certain Tinseltown quality from her sheer youth.

Conceivably, Franklin could win all seven events and then immediately embark upon her freshman year at Berkeley, where she is most preoccupied with the thought of missing her mother and father. “Don’t talk about it, I’ll start crying,” she protests, when the prospect is mentioned. “My parents are my best friends and I’m going to miss them so much.”

Few in sport marry these traits of wide-eyed likeability and prodigious inbuilt ability quite so convincingly. Swimming needs her, not solely to serve as its poster-girl but to redraw its possibilities in the post-Phelps landscape.

After Wednesday night’s victory in the 200m free she is three-sevenths of the way to attaining her goal. No woman has yet garnered seven golds at a single Worlds, and Franklin, with four Olympic triumphs already cementing her as London 2012’s most garlanded woman, has the time and talent to push the boundaries further.

The only agony is that her withdrawal from the backstroke taints, a little, the pristine quality of the achievement she coveted in Barcelona. For the fascination of sport thrives upon the notion of immaculate supremacy.

It is the reason why we were impatiently ticking off Frankin’s eight rungs of the ladder, the reason why we hope that South Korea’s Inbee Park can become the first professional golfer to claim four major titles in a calendar year at St Andrews.

It is why we still invoke with a certain shudder Don Bradman’s ever-so-nearly Test average of 99.94, why a mortal sigh resounded around Trent Bridge when Ashton Agar holed out on 98, short of anointing himself as the first No 11 to make a Test century – on debut, too.

And it is why Usain Bolt, the one man apparently with no records left to break, announced on Wednesday that for his next trick he would target a sub-19-second 200m race. For the finest scripts – as Franklin illustrates – depend on a Rubicon being crossed, on a capacity to amaze.